| 时间 | 值 （亿美元） | 世界排名 |
|---|---|---|
| 2016 | 0.8 | 66 |
| 2015 | 1.1 | 152 |
| 2014 | 0.9 | 153 |
| 2013 | 0.5 | 162 |
| 2012 | 0.6 | 167 |
| 2011 | 0.6 | 164 |
| 2010 | 0.1 | 180 |
| 2009 | 0.9 | 149 |
| 2008 | 0.1 | 179 |
| 2007 | 0.8 | 164 |
| 2006 | 0.2 | 172 |
| 2005 | 0.3 | 158 |
| 2004 | 0.6 | 146 |
| 2003 | 0.4 | 144 |
| 2002 | 0.3 | 141 |
| 2001 | 0.3 | 134 |
| 2000 | 0.3 | 136 |
| 1999 | 1.6 | 92 |
| 1998 | 2.6 | 81 |
| 1997 | 2.7 | 77 |
| 1996 | 2.9 | 66 |
| 1995 | 2.8 | 59 |
| 1994 | 0.2 | 116 |
| 1993 | 0.1 | 119 |
| 1992 | 0 | 131 |
| 1991 | 0.1 | 110 |
| 1990 | 0.2 | 95 |
| 1989 | 0.1 | 85 |
| 1988 | 0.2 | 76 |
| 1987 | 0.1 | 98 |
| 1986 | 0 | 100 |